High-density recording on multiple tracks of a magnetic tape is known. In certain arrangements, parallel tracks extend along a longitudinal direction of the magnetic tape. Magnetic tape is moved transversely across a magnetic head so that a read and/or write element of the magnetic head is moved in proximity to the desired track. During recording or playback, the read/write elements of the head should be aligned with the desired track as the tape moves in a longitudinal direction across the read/write bump. To increase storage capacities, track density, which is the number of tracks per distance (e.g., inches), has gradually increased. As this track density increases, the track pitch and width decrease. For proper read/write operation, the read/write element of the magnetic head should stay at, or very near, the center line of the track. Due to this reduced track pitch, improvements to the head positioner are needed to minimize the offset between the read/write elements of the head and the center line of the track. To that end, servo-based tracking systems employed to allow the tape drive to monitor the head-to-track relationship. If the drive determines that the head and track are offset, then the head positioner corrects the relative position to maintain the relationship between the head and the center line of the track.
Closed loop positioners are often used in tape systems having higher track densities. In high-density tape systems, the tape may wander in the lateral direction as it moves in the longitudinal direction, which results in an offset between the magnetic head and the track center line. To avoid these types of problems, tape cartridges for high-density tape drives are preformatted with information often called servo information, which is used to maintain the correct lateral position of the tape with respect to the magnetic head. Servo information provides the system with feedback to determine the continuous position of the tape relative to the head. Analysis of the servo signals allows for a determination of an offset and the distance of the offset between the track and the head. Based on the information, the head is moved by a positioner to the center line of the track so that write/read operations can occur properly. Closed loop positioners generally use fine positioners to move the head during a write/read operation. These fine positioners are used to maintain the position of the head at the center line of the track under a closed loop servo control using the preformatted servo information on the tape.
The tracking servo system employed by linear tape drives, such as the Linear Tape Open (“LTO”) family, is an example of a servo-based, closed loop control mechanism that allows for increased track density. Track density is one of the parameters, besides bit density, that allows storage capacity to increase. The tracking servo system requires feedback to indicate the relative position of the tape and the recording head elements. One of the methods employed in linear tape drives using such feedback signals is to pre-record a series of magnetic stripes that contain position feedback information, which is a timing-based signal. When the stripes are recorded with predetermined azimuth angles, the signals from the head can be processed to decode the lateral position information regarding the relative position of the head and the tape.
The decoding of the lateral position information is based on timing of the detected pulses. As the magnetic head moves from one track on the tape to another, the timing of the pulses changes indicating the position feedback signal. Variations in a tape travel path relative to the magnetic head will typically lead to read after write (“RAW”) errors. RAW errors can occur because a read bump, on the magnetic head, used to verify data written by an adjacent write bump, will be reading at a location on the tape where data was not written by the write bump.
In view of the foregoing, a need exists in the art for tape drives that accurately re-position the magnetic head when the tape travel path changes.
The foregoing examples of the related at and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.